The Appearance of Specific Helper Cells in Lymph of Immunized Sheep

Abstract

Culture conditions which support the induction by antigen of plaque-forming cells (PFCs) in cell suspensions made from lymph nodes from sheep do not support the induction of PFCs in suspensions of non-primed lymphocytes obtained from the efferent lymph of a lymph node. The lymphocytes in the efferent lymph of a node after immunization with heterologous erythrocyte antigen, via an afferent lymphatic vessel, however, respond in vitro to the specific antigen with the generation of PFCs. Immune responses were confined to single lymph nodes, and the lymphocytes of the efferent lymph issuing from these were added to nonimmunized efferent lymph cells of other nodes in the same sheep. It was found that the addition of low numbers of immunized T lymphocytes to saturating numbers of nonimmune lymphocytes, either unseparated, or the B cell fraction only, gave rise in cultures stimulated with the specific antigen to PFCs in numbers comparable to those induced in cultures containing only saturating amounts of immunized lymph node lymphocytes. Immunized B cells were not capable of providing help. The specific helper T cells required were found to be recirculating between blood and lymph for several months after immunization. Irradiated T cells were not capable of providing sufficient help. The number of lymphocytes forming rosettes with chicken red blood cells or horse red blood cells in efferent lymph increases after immunization of a sheep lymph node through an afferent lymphatic vessel with specific antigens. Rosette-forming cells (RFCs) were removed by Ficoll-Isopaque flotation and the properties of the RFCs were determined in the culture system. It was found that specific B precursor cells were antigen binding because the response in vitro was abolished after these rosette-forming B cells had been removed. Helper T cells appearing in the efferent lymph subsequent to immunization were found not to be antigen binding because T cells issuing from immunized lymph nodes, after removal of RFCs, were still capable of providing specific help to a nonimmunized B cell population.